This invention relates to a solid state sensor and, in particular, to a solid state sensor wherein a semiconductive coating is fused onto a support material.
More specifically, this invention relates to a solid state sensor for detecting small amounts of ozone in an atmosphere, such as ambient air, without interference from background gases that might be present in the atmosphere, and is an improvement of the sensor disclosed in a pending application, Ser. No. 888,228 filed Mar. 20, 1978.
A gas detector that uses a thin film metal oxide is disclosed in U.S. Pat. No. 3,778,229. However, thin film elements of this nature exhibit an extremely high impedance and are highly susceptible to thermal and random noise. As a consequence, these devices do not lend themselves for use in most practical electronic circuits. The sensitivity of most thin film elements is also relatively low due to the compactness of the semiconductive material and the limited amount of surface area that can be presented to the sampled atmosphere. It is further noted that the equipment required to carry out any type of thin film technology is generally costly and complex which, of course, affects the cost of the products so produced.
Other sensors, particularly those used to detect the presence of reducing gases, have been produced in thick film configurations by means of sintering processes or the like. Although exhibiting a lower impedance than their thin film counterparts, many thin film elements still are slow to respond to oxidizing gases and equally slow to recover once they have been oxidized. As a consequence, these sensors cannot be readily cycled and recycled in a continuous and/or automated sensing system.
Another disadvantage associated with many solid state sensors, both thin film and thick film, is the difficulty encountered in placing the semiconductive coating upon a suitable substrate or support material. Because of the nature of the materials involved, a relatively weak bond is oftentimes formed at the material interface whereupon the semiconductor can flake away from the support or be damaged by ordinary handling.